Spring ApplicationContext（五）BeanFactoryPostProcessor

产生回顾一下 ApplicationContext 初始化的几个步骤：第一步是刷新环境变量；第二步是刷新 beanFactory 并加载 BeanDefinition；第三步是对 beanFactory 进行功能扩展，如增加 SPEL 支持和属性编辑器；第四步是留给子类实现的。

本节关注的是第五步：注册 BeanFactoryPostProcessor 并执行。

public void refresh() throws BeansException, IllegalStateException {
    // 5. 注册并执行 BeanFactoryPostProcessor 后置处理器
    invokeBeanFactoryPostProcessors(beanFactory);
}

BeanFactoryPostProcessor 接口如下：

public interface BeanFactoryPostProcessor {
    // All bean definitions will have been loaded, but no beans will have been instantiated yet
    void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

一、BeanFactoryPostProcessor 应用

1.1 典型应用：PropertyPlaceholderConfigurer

@Value("${age}")
private int age;

xml 配置如下：

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations">
        <list>
            <value>classpath:conf.properties</value>
        </list>
    </property>
</bean>

很显然属性注入 beanFactory 是在 beanDefinition 加载完成，即将进行 bean 的加载之前，PropertyPlaceholderConfigurer 实现了 BeanFactoryPostProcessor 接口来完成这一步的工作。

源代码【PropertyResourceConfigurer】

public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
    try {
        // 1. 将环境变量和 properties 
        Properties mergedProps = mergeProperties();

        // 2. Convert the merged properties, if necessary.
        convertProperties(mergedProps);

        // 3. 将解析后的属性注册到 Spring 工厂中
        processProperties(beanFactory, mergedProps);
    }
    catch (IOException ex) {
        throw new BeanInitializationException("Could not load properties", ex);
    }
}

1.2 自定义 BeanFactoryPostProcessor

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;

import java.util.Arrays;

@Component
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        int singletonCount = beanFactory.getSingletonCount();
        String[] singletonNames = beanFactory.getSingletonNames();

        System.out.println("BeanFactoryPostProcessor 执行 postProcessBeanFactory() 方法");
        System.out.println("singletonCount：" + singletonCount);
        System.out.println("singletonNames：" + Arrays.asList(singletonNames));
    }
}

运行后结果如下：

BeanFactoryPostProcessor 执行 postProcessBeanFactory() 方法
singletonCount：6
singletonNames：[environment, systemProperties, systemEnvironment, org.springframework.context.annotation.internalConfigurationAnnotationProcessor, org.springframework.context.annotation.ConfigurationClassPostProcessor.importRegistry, myBeanFactoryPostProcessor]

二、BeanFactoryPostProcessor 注册及执行

源代码【AbstractApplicationContext】

public void refresh() throws BeansException, IllegalStateException {
    // 5. 注册并执行 BeanFactoryPostProcessor 后置处理器
    invokeBeanFactoryPostProcessors(beanFactory);
}

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
}

源代码【PostProcessorRegistrationDelegate】

public static void invokeBeanFactoryPostProcessors(
        ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

    // Invoke BeanDefinitionRegistryPostProcessors first, if any.
    Set<String> processedBeans = new HashSet<String>();

    // 省略 ... 
    // 执行 BeanDefinitionRegistryPostProcessors 的 postProcessBeanDefinitionRegistry() 方法

    // 1. 筛选出 BeanFactoryPostProcessor 类的类名称，并按 PriorityOrdered、Ordered、nonOrdered 执行
    String[] postProcessorNames =
            beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

    List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    List<String> orderedPostProcessorNames = new ArrayList<String>();
    List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
    for (String ppName : postProcessorNames) {
        if (processedBeans.contains(ppName)) {
            // skip - already processed in first phase above
        }
        else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
        }
        else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
            orderedPostProcessorNames.add(ppName);
        }
        else {
            nonOrderedPostProcessorNames.add(ppName);
        }
    }

    // 2. 执行 PriorityOrdered.
    sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

    // 3. 执行 Ordered.
    List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    for (String postProcessorName : orderedPostProcessorNames) {
        orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    sortPostProcessors(beanFactory, orderedPostProcessors);
    invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

    // 4. 执行 nonOrdered
    List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    for (String postProcessorName : nonOrderedPostProcessorNames) {
        nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

    // Clear cached merged bean definitions since the post-processors might have
    // modified the original metadata, e.g. replacing placeholders in values...
    beanFactory.clearMetadataCache();
}

private static void invokeBeanFactoryPostProcessors(
        Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {

    for (BeanFactoryPostProcessor postProcessor : postProcessors) {
        postProcessor.postProcessBeanFactory(beanFactory);
    }
}

每天用心记录一点点。内容也许不重要，但习惯很重要！

Spring 容器 ApplicationContext（五）BeanFactoryPostProcessor

原文：https://www.cnblogs.com/binarylei/p/10423552.html